DESCRIPTION: (Investigator's Abstract) Previous work has shown that laryngeal reflexes may be studied non-invasively in humans by analyzing involuntary changes in the voice fundamental frequency (Fo) in response to stimulation of cranial sensory nerves. The present study uses this methodology to analyze trigemiono laryngeal reflexes (TLRs) in stutterers and normal speakers. Impetus for the study comes from suggestions that the coordination of articulatory and phonatory movements during normal speech, and the disintegration of speech control during stuttering may involve TLR mechanisms. Since very little is known about these mechanisms, the purpose of the present study is to provide a more detailed description of the properties of the TLRs and to assess their relevance to models of normal and abnormal speech production. Subjects will be serve and non-severe idiopathic stutters (N>40) and normal speakers (N>40), between the ages of 20 and 45. They will sustain vowel phonation at constant voice fundamental frequency (Fo) or will modulate their Fo in a sinusoidal fashion while receiving brief or sinusoidally modulated mechanical stimuli (tissue deformation) applied to the upper lip. The stimuli will be of different force magnitudes (5, 10, 15, 20 gr) and will be delivered with a servo-controlled probe. The Fo will be transduced with a neck accelerometer and a frequency meter yielding a voltage proportional to Fo. Computer aided signal averaging, spectral analysis, and coherence and cross correlation analysis techniques will be used to study the temporal, amplitude, and spectral characteristics of the Fo responses. These responses will be compared across stutters and non-stutters and in relation to the characteristics of the stimuli and phonatory conditions. Results from this study could provide important information on the characteristics of the TLRs and the significance of these reflexes to normal speech control, to stuttering, and to other speech disorders. Results should also lead to improved methods of assessing the integrity of the nervous system and to better diagnostic and therapeutic procedures of speech disorders.